Resting Energy Expenditure in Adults With Williams Syndrome: Comparative Accuracy of Predictive Equations.

Adults with Williams syndrome had lower measured resting energy expenditure (mREE) than BMI-matched controls, with differences largely explained by fat-free mass.

• Males with WS had mREE of 1310.0 ± 164.7 kcal/day vs. 1653.5 ± 406.7 kcal/day in male controls.
• Females with WS had mREE of 1163.1 ± 123.5 kcal/day vs. 1377.4 ± 401.5 kcal/day in female controls.
• After adjusting for fat-free mass (FFM), differences in mREE between WS participants and matched controls were no longer statistically significant.
• 24 adults with WS were matched to concurrent or historical controls on age, sex, race/ethnicity, and BMI; analyses used independent samples t-tests (unadjusted) and ANCOVA (adjusted).

Within the Williams syndrome cohort, mREE was significantly lower in females than in males, a difference that persisted but with attenuated significance after adjusting for FFM.

• Mean mREE in females with WS was 1183.1 ± 186.6 kcal/day compared to 1366.4 ± 217.8 kcal/day in males with WS.
• After adjusting for FFM, the sex-based difference in mREE persisted but with attenuated significance.
• The cohort consisted of 41 adults with WS (mean age 31.5 ± 10.2 years, mean BMI 28.6 ± 7.7 kg/m²).
• mREE was measured using indirect calorimetry at a clinical research centre.

Adults with Williams syndrome and a BMI ≥ 30 kg/m² had higher mREE than those with BMI < 30 kg/m², but this difference was no longer significant after adjusting for FFM.

• The difference in mREE between BMI categories (< 30 vs. ≥ 30 kg/m²) reached statistical significance in unadjusted analyses.
• After adjusting for FFM, the difference between BMI categories no longer reached significance.
• Body composition was assessed using dual energy X-ray absorptiometry (DXA) to obtain FFM and fat mass (FM).

Most widely used predictive resting energy expenditure equations failed to achieve clinically acceptable accuracy thresholds in adults with Williams syndrome.

• Most predictive equations did not achieve ≥ 70% individual-level accuracy or a mean absolute percentage error ≤ 10%.
• Predictive equations were derived from several distinct adult populations, including some with adults ages 60 and older and others with a high proportion of adults with overweight or obesity.
• pREE was computed and prediction accuracy assessed at both individual and group levels for each equation.

The Mifflin FFM equation was the highest-performing predictive equation for adults with Williams syndrome, achieving the best individual-level accuracy rates.

• The Mifflin FFM equation yielded individual accuracy rates of 87.5% in males and 68.0% in females with WS.
• The second top-performing equations differed by sex: Owen FFM achieved 68.8% individual accuracy in males, and Bernstein Height & Weight achieved 64% individual accuracy in females.
• More accurate predictions tended to originate from equations developed in cohorts with a high prevalence of overweight and obesity or with older adults.

Fat-free mass was identified as the primary factor explaining mREE differences both between sexes within the Williams syndrome cohort and between Williams syndrome participants and matched controls.

• FFM was retained as a covariate in ANCOVA models examining sex differences and WS vs. control differences in mREE.
• Age was retained in all models even though it was not a significant predictor.
• Previous research indicates adults with WS have decreased fat-free mass on body composition analysis, which contextualizes these findings.

The study found that no prior explorations of factors associated with measured REE or accuracy of predictive REE equations had been performed in adults with Williams syndrome.

• Williams syndrome is a rare neurodevelopmental disorder caused by a microdeletion on chromosome 7q.
• Previous research indicates adults with WS are prone to overweight and obesity and have decreased fat-free mass on body composition analysis.
• This study is described as the first to obtain mREE in adults with WS, examine contributing factors, compare mREE to matched controls, and assess accuracy of predictive equations.